NCERT Solutions for Class 12 Physics Chapter 12 – Atoms

NCERT Solutions for Class 12 Physics Chapter 12 – Atoms will ensure that you are well-versed with the chapter and have a thorough revision of all the NCERT questions. The chapter covers various topics like the Balmer series, Lyman series, Brackett series, Neil Bohr’s atomic model and Rutherford’s scattering experiment. There are 17 exercise questions in the chapter. Most of them are numerical-based questions. 

Our NCERT Solutions aim that all your doubts are resolved at one place and you’re not stuck in the chaos of finding various resources. All the solutions are as per the latest CBSE syllabus and ensure that you are fully prepared for the exams. The solutions are 100% correct and include all the explanations of the concepts of the chapter.

Important Topics of NCERT Solutions for Class 12 Physics Chapter 12 – Atoms

Rutherford’s Nuclear Model of Atom 

NCERT Solutions for Class 12 Physics Chapter 12 talks about the atomic model which was prepared by Rutherford after his experiment of scattering an alpha particle. In his atomic model, he stated that the entire positive charge and most of the mass of the atom are concentrated in the nucleus and the electron is situated at a certain distance away from it. 

Rutherford further explained that the electrons are moving in orbits around the nucleus and then suggested the size of the nucleus based on his experiment. The chapter will give you graphical, mathematical and theoretical information about his model and the postulates which were used to derive other fundamentals related to the experiment and atoms at large. 

Atomic Spectra 

You will learn about a spectrum which consists of the characteristic radiations which are emitted by the elements. Whenever an atomic gas or a vapour gets at an excited state at low pressure, while current is passed through it, the emitted radiation has a spectrum which contains certain specific wavelengths. Such a spectrum is termed as an emission line spectrum and it comprises a bright line in its dark background. 


The chapter will introduce you to line spectrums which are omitted by hydrogen and their series is known as line spectrum series. Their frequencies are expressed in various terms like:

  • The Lyman series 
  • The Balmer series
  • The Paschen series 
  • The Brackett series
  • The Pfund series

Neil Bohr’s Model of Hydrogenic Atoms 

Neil Bohr proposed a model of Hydrogenic Atoms and presented three postulates for its quantum mechanics. Those three postulates are given as follows – 

  • The electrons in a hydrogen atom revolve in a particular and stable orbit and this happens without any radiant energy emission.
  • The orbits in which the angular momentum is an integral multiple of h/2π are known as stationary orbits and this condition is termed as Bohr’s quantization condition. Here L = nh/2π. And here n is an integer which is termed to be a quantum number. 
  • In his third postulate, Bohr stated that an electron might make a transition from one of its specified non- radiating orbits to another one with a lower energy. And when an orbit does so, a photon is emitted and it has the energy which is equal to the energy difference between the initial and the final states. The frequency of the emitted photon is then written as: Hv = Ei – Ef 

Exercise Discussion of NCERT Solutions for Class 12 Chapter 12 – Atoms

  • The first question of the NCERT Class 12 Physics Chapter 12 is a short-answer type question where you have to fill in the blanks. 
  • Question 12.2 is also very simple and aims at testing your application skills and observation using which you need to provide the results of the alpha particle scattering experiment. 
  • The exercise also has a fair share of numerical questions like question 12.6 where you have been provided with the value of the energy level of a hydrogen atom and you are required to derive the frequency and the wavelength of the photon. The question is a bit lengthy but it is not very complex and requires just the basic understanding of the chapter, along with the correct formulas. 
  • Question 12.7 is also similar and requires you to calculate the speed of the hydrogen atom based on its energy level and the orbital period of each of these levels. 
  • Question 12.9 requires you to detect the series of wavelengths of an electron; here you need to apply the formula of orbital energy in order to derive the answer. Such questions can be important from an exam point of view and can fetch you a good score as well. 

Benefits of NCERT Solutions for Class 12 Physics Chapter 12 – Atoms

Instasolv’s NCERT Solutions for Class 12 Chapter 12 are the best study resource for CBSE exam preparation. We have checked every answer at various levels to ensure that what you receive is a high-quality solution. We have explained the formulae and all the laws related to this chapter clearly. These solutions are ideal for revising the basics of atoms for competitive exams like JEE Main and NEET.